mapAsyncIterator-test: check that return value is passed on early return (#3066)

Author: IvanGoncharov

src/subscription/__tests__/mapAsyncIterator-test.js

@@ -90,11 +90,16 @@ describe('mapAsyncIterator', () => {
 
   it('allows returning early from mapped async generator', async () => {
     async function* source() {
-      yield 1;
-      yield 2;
+      try {
+        yield 1;
+        yield 2;
 
-      // istanbul ignore next (Shouldn't be reached)
-      yield 3;
+        // istanbul ignore next (Shouldn't be reached)
+        yield 3;
+      } finally {
+        // eslint-disable-next-line no-unsafe-finally
+        return 'The End';
+      }
     }
 
     const doubles = mapAsyncIterator(source(), (x) => x + x);
@@ -104,7 +109,7 @@ describe('mapAsyncIterator', () => {
 
     // Early return
     expect(await doubles.return()).to.deep.equal({
-      value: undefined,
+      value: 'The End',
       done: true,
     });
 

src/subscription/mapAsyncIterator.js

@@ -4,16 +4,16 @@ import type { PromiseOrValue } from '../jsutils/PromiseOrValue';
  * Given an AsyncIterable and a callback function, return an AsyncIterator
  * which produces values mapped via calling the callback function.
  */
-export function mapAsyncIterator<T, U>(
-  iterable: AsyncIterable<T> | AsyncGenerator<T, void, void>,
+export function mapAsyncIterator<T, U, R = void>(
+  iterable: AsyncGenerator<T, R, void> | AsyncIterable<T>,
   callback: (T) => PromiseOrValue<U>,
-): AsyncGenerator<U, void, void> {
+): AsyncGenerator<U, R, void> {
   // $FlowIssue[incompatible-use]
   const iterator = iterable[Symbol.asyncIterator]();
 
   async function mapResult(
-    result: IteratorResult<T, void>,
-  ): Promise<IteratorResult<U, void>> {
+    result: IteratorResult<T, R>,
+  ): Promise<IteratorResult<U, R>> {
     if (result.done) {
       return result;
     }
@@ -37,7 +37,7 @@ export function mapAsyncIterator<T, U>(
     async next() {
       return mapResult(await iterator.next());
     },
-    async return(): Promise<IteratorResult<U, void>> {
+    async return(): Promise<IteratorResult<U, R>> {
       return typeof iterator.return === 'function'
         ? mapResult(await iterator.return())
         : { value: undefined, done: true };